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Space junk

There are 20,000 pieces of debris larger than a softball cluttering the Earth's lower orbit. Photo: NASA

News broke Tuesday that the International Space Station had come under close attack, but not by evil space villains. Instead, a piece of space debris moving at more than 20,000 miles per hour nearly wiped out the station and its six-member crew. Tuesday marked the second time that crew members took refuge in Soyuz “lifeboat” capsules. There was a near miss with a satellite motor in 2009.

Otherwise known as “space junk,” this intergalactic trash does not contain your run-of-the-mill discards. According to NASA, it includes nonfunctional spacecraft, such as satellites that have completed their tours; abandoned propeller rockets that help lift spacecraft off Earth; mission-related debris, such as a wrench that falls from an astronaut’s hand during a repair; and fragmentation debris from objects colliding and exploding in orbit. Space junk primarily flies at low Earth orbit — 300 to 2,000 kilometers above Earth’s surface — and can be bothersome. Here’s why.

1. We can’t clean it up.

The low Earth orbit is basically a trash dump that, for now, can’t be emptied. Without gravity, these objects remain in orbital motion, impossible to slow down and impossible to contain. Although the junk cannot be trapped and discarded, some of it can be tracked.

There are more than 20,000 pieces of space junk that measure larger than a softball, and these are tracked by the Department of Defense. Together, both NASA and DoD use ground-based sensors to survey each object’s orbit.

However, there are many millions of smaller discards that cannot be tracked. These items can either be small objects, such as individual bolts from broken pieces, or fragments of larger objects that broke off in earlier collisions.

2. It moves fast.

To stay in the lower Earth orbit, objects need to move at a pretty good clip. How fast? Roughly 17,000 mph, give or take 1,000. Even the small objects in orbit, such as a bolt or a paint chip, can cause damage. When colliding with another object in motion, the combined speed can reach 20,000 mph.

The direction in which an object is moving poses another problem. Generally, objects in the low Earth orbit travel from pole to pole, but not in a uniform path, as is the case in other orbits. Pieces of junk fly out at others that are speeding in the opposite direction. The likelihood of collision increases, and the result can be explosive.

3. It’s increasing.

Recent collisions, though few, have contributed to a space junk buildup. A 2007 anti-satellite test initiated by the Chinese, which sent a missile into space to obliterate an old weather satellite, added more detritus to the problem — more than 3,000 broken fragments, according to NASA. In addition, a 2009 collision between a nonfunctional Russian satellite and a functional American commercial satellite contributed 2,000 more pieces to the floating junkyard.

Previous theories about cleaning up space junk emphasized the importance of orbital collisions, the idea being that individual pieces of debris would become so small they wouldn’t be of concern. Now, scientists at the Union of Concerned Scientists, a nonprofit organization, believe the presence of millions of little pieces worsen the litter situation: it increases the amount of junk that can’t be tracked, and could make it too dangerous to use parts of space.

4. It can enter Earth’s atmosphere.

Those homesick pieces of space junk close enough to Earth’s atmosphere can sometimes return home. Objects have re-entered Earth and hit solid ground. But not to alarm anyone: This scenario is pretty rare. Generally, if the debris is small and it enters Earth’s atmosphere, it burns up. In this regard, the atmosphere acts as a vacuum cleaner.

5. But significant collision with human spacecraft is unlikely.

Thanks to NASA and DoD surveillance, major collisions with human spacecraft stand a low chance. Tuesday marked the second time the International Space Station crew had to hunker down in Soyuz ships. Generally, scientists know well beforehand if a collision is to occur with the help of handy formulas and diagrams.

If an object approaches a spacecraft or a satellite, mission control issues warnings and tells individual stations and satellite operators to change their current locations with good time to spare.

But this doesn’t mean that collisions never happen. If any structure is in space long enough, it will get hit by something, but it doesn’t usually have humans on board.